Lecture #7 Voltage Regulators

Instructor: Dr. Ahmad El-Banna

Benha University Faculty of Engineering at Shoubra

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ECE-322 Electronic Circuits (B)

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Agenda

Voltage Regulation

Basic Linear Series Regulators

Basic Linear Shunt Regulators

Intro. to Switching Regulators 2

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VOLTAGE REGULATION 3

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Intro.

• Two basic categories of voltage regulation are:

• Line regulation

• Load regulation

• The purpose of line regulation is to maintain a nearly constant output voltage when the input voltage varies.

• The purpose of load regulation is to maintain a nearly constant output voltage when the load varies.

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Line Regulation

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• When the ac input (line) voltage of a power supply changes, an electronic circuit called a regulator maintains a nearly constant output voltage.

• Line regulation can be defined as the percentage change in the output voltage for a given change in the input voltage

• Line regulation can also be expressed in units of %/V

Load Regulation

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• Load regulation can be defined as the percentage change in output voltage for a given change in load current.

• One way to express load regulation is as a percentage change in output voltage from no-load (NL) to full-load (FL).

• The load regulation can be expressed as a percentage change in output voltage for each mA change in load current.

• Using ROUT, Thevenin equivalent circuit for a power supply with a load resistor.

BASIC LINEAR SERIES REGULATORS 7

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Regulators Classification

• The fundamental classes of voltage regulators are:

• linear regulators

• switching regulators

• Both of these are available in integrated circuit form.

• Two basic types of linear regulator are

• series regulator

• shunt regulator

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Series Voltage Regulator

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Basic op-amp series regulator

Regulating Action

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• Illustration of series regulator action that keeps VOUT constant when VIN or RL changes.

Short-Circuit or Overload Protection

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• If an excessive amount of load current is drawn, the series-pass transistor can be quickly damaged or destroyed.

• Most regulators use some type of excess current protection in the form of a current-limiting mechanism.

• one method of current limiting to prevent overloads called constant-current limiting.

BASIC LINEAR SHUNT REGULATORS 12

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Shunt Regulator

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• In the shunt regulator, the control element is a transistor in parallel (shunt) with the load.

Regulating Action

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• Sequence of responses when VOUT tries to decrease as a result of a decrease in RL or VIN (opposite responses for an attempted increase)

• It offers inherent short-circuit protection

INTRO. TO SWITCHING REGULATORS 15

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Switching Regulators

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• The two types of linear regulators, series and shunt, have control elements (transistors) that are conducting all the time, with the amount of conduction varied as demanded by changes in the output voltage or current.

• The switching regulator is different because the control element operates as a switch.

• A much greater efficiency can be realized with a switching type of voltage regulator than with the linear types because the transistor switches on and off and dissipates power only when it is on.

• Efficiencies can be greater than 90%.

• Three basic configurations of switching regulators are step-down, step-up, and inverting.

• In some cases, such as a laptop computer, all three types may be employed for various parts of the system.

• For example, the display typically will use an inverting type, the microprocessor would use a step-down type, and the disk drive may use a step-up type.

• For more details, refer to:

• Chapter 17, T. Floyd, Electronic Devices, 9th edition.

• The lecture is available online at:

• http://bu.edu.eg/staff/ahmad.elbanna-courses/12135

• For inquires, send to:

• ahmad.elbanna@feng.bu.edu.eg

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